In some motor vehicle air-conditioning systems, thermal adsorption may be used instead of compression. Thermal-adsorption air-conditioning systems use an adsorbent chemical (e.g. zeolite, silica gel, activated carbons) rather than a mechanical compressor, and are driven by thermal energy rather than mechanical work. For example, a thermal-adsorption air-conditioning system in a motor vehicle may be driven by waste exhaust heat from the vehicle's engine, whereas the compressor used in many conventional air-conditioning systems may be driven by the engine crankshaft and may exert a load on the engine. As such, air-conditioning systems utilizing thermal adsorption instead of a compressor may advantageously achieve reduced engine loading and reduced fuel consumption.
One cycle of operation of a thermal-adsorption air-conditioning system includes the adsorption of a refrigerant, e.g. water, onto a solid adsorbent, e.g. zeolite (during what is referred to herein as “adsorbing mode”), and the subsequent desorption of the refrigerant from the adsorbent (during what is referred to herein as “desorbing mode”). This process may occur in a canister referred to as an adsorber. During the adsorbing mode, the adsorbent is actively cooled, for example via a cool heat transfer fluid (HTF). The cooling of the adsorbent creates suction, such that vaporized refrigerant is drawn into the adsorber and adsorbed by the adsorbent. In a common application, the refrigerant is drawn into the adsorbent from an evaporator via the suction, such that it evaporates from the evaporator and thereby cools the evaporator. In contrast, during the desorbing mode, the adsorbent is actively heated, for example via a hot HTF. The heating of the adsorbent causes the refrigerant to be desorbed from the adsorbent. In a common application, the refrigerant flows into a condenser after being desorbed from the adsorbent, such that it condenses at the condenser and thereby heats the condenser.
US 2011/0005267 describes an automobile air-conditioning system including a thermal-adsorption heat pump which operates in conjunction with a condenser and evaporator in the manner described above. The thermal-adsorption heat pump is powered by engine exhaust heat, and includes at least two adsorbers which adsorb and desorb refrigerant cyclically and asynchronously. In one embodiment, the system includes three working fluid loops: an HTF loop for heating/cooling the adsorbers where the working fluid is a mineral-oil-based HTF, an adsorption loop entirely exterior to the passenger cabin where the working fluid may be NH3, and a refrigerant loop transferring heat from the cabin to the adsorption loop (via an inter-loop heat exchanger) where the working fluid may be R-134a.
The HTF loop heats/cools the adsorbers to effect adsorption/desorption at the adsorbents within the adsorbers. Cool HTF for the adsorbing mode is provided by an HTF cooler, and hot HTF for the desorbing mode is provided by an HTF heater. Thermal reservoirs storing exhaust heat in phase change material (PCM) are coupled with the HTF heater. The adsorption loop includes NH3 which is adsorbed/desorbed from the adsorbents in the adsorbers. After the engine is shut off, heat stored in the thermal reservoirs is used to desorb NH3 from the adsorbents into a reservoir. NH3 stored in the reservoir is then used to provide “surge cooling” after engine cold start, while HTF in the HTF loop is still being heated, in order to start thermally cycling the adsorbers and pumping refrigerant. To provide cooling to the cabin, a heat exchanger is coupled with the refrigerant loop and the adsorbent loop. At the heat exchanger, R-134a from the refrigerant loop condenses, while NH3 from the adsorbent loop evaporates. The refrigerant loop further includes an R-134a evaporator communicating with the cabin to provide cooling to the cabin via a blower.
However, the inventors have recognized various issues with the above-described system. In order to provide surge cooling at engine start, NH3 is stored in a pressurized reservoir in the above system. Even ignoring the safety hazards associated with storage of pressurized NH3, a pressurized reservoir may be costly in terms of materials and in terms of the space it takes up in the vehicle. Further, an undesirably large reservoir may be required to store enough NH3 to meet surge cooling needs during hot weather conditions. Furthermore, it may not be possible to downsize the adsorbers used in the system due to the constraints of the pressurized NH3 reservoir, and therefore it may not be possible to improve the efficiency of adsorber operations and/or ensure that the system is packagable in motor vehicles.
To address these issues, among other issues, the inventors herein have identified a climate control system incorporating thermal adsorption in conjunction with a standalone cold PCM battery and a standalone hot PCM battery, and methods for its operation. In one example, a method for a vehicle climate control system includes, during a summer mode, driving two adsorbers with HTF heated by engine exhaust in a hot HTF circuit and HTF cooled by an HTF cooler in a cold HTF circuit, and charging a standalone cold phase PCM battery communicating with the adsorbers. The method further includes, during a winter mode, coupling the hot HTF circuit with a heater core.
In this way, by charging a standalone cold PCM battery during summer mode operation of the climate control system, thermal energy may be stored in the battery for use in a surge cooling mode at a subsequent engine start. Because of the advantages of PCM storage of thermal energy (e.g., as opposed to storing thermal energy via pressurized NH3), it may be possible to downsize the adsorbers, thereby improving packagability of the climate control system and thermal adsorption efficiency. Further, a hot PCM battery may be included in the climate control system to provide surge heating during winter mode operation of the climate control system. Accordingly, downsized adsorbers may be sufficient for winter mode operation of the climate control system as well.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.